Solving Problems Without Paper

Date: 9/1/95 at 19:9:51
From: Megan Lee Mead
Subject: working problems in my head
My name is Megan Mead. I'm in seventh grade and I'm having trouble
when we have to do problems in our head instead of on paper. Do you have
some ideas on what will help me?

Date: 9/2/95 at 11:47:11
From: Doctor Ken
Subject: Re: working problems in my head
Hello!
To tell you the truth, I'm actually not all that good at doing numbers in my
head either. I have gotten better at it though, and here's what has helped
me.
I don't try to do the addition and multiplication the way that people learn
in school, starting on the right and working toward the left. I actually
start on the left and go right. I find it easier because you don't have to
remember the numbers in the reverse order you really want them in. For
example, if we had 342 + 831, here would be my steps:
342
+831
----
11
342
+831
----
117
342
+831
----
1173
The only weird part is when you have to carry numbers. Then you have to go
back and change what you had before:
746
+487
----
11
746
+487
----
122
746
+487
----
1233
I do the same thing for multiplication, but that gets a little more tricky
to remember all the steps. Can you figure out how to do that?
-Doctor Ken, The Geometry Forum